U.S. Pat. No. 7,277,570, which is incorporated herein by reference, describes image processing techniques to determine as-sprayed drop statistics for sprayed witness cards (WCs). As described therein, a wide variety of manufacturing and agricultural processes rely upon the use of instrument controlled spraying. For example, farmers and foresters typically use aircraft and/or farm equipment equipped with instrument sprayers to apply fertilizers and pesticides. Manufacturers use spray techniques to apply coatings and/or layers of a prescribed density and/thickness.
In the case of farming and forestry, the spraying process preferably results in a prescribed amount of fertilizer or pesticide being distributed uniformly to the ground, crop or trees. A spray that distributes too little fluid to a target area may reduce the effectiveness of the fertilizer or pesticide treatment, resulting in lost crops/trees and/or reduced yield. A spray that distributes too much fluid to a target area typically increases the cost of applying the treatment and may result in additional losses due to undesired side effects and/or pollution. A spray that distributes fluid to a target area unevenly, typically results in some portions of the sprayed area receiving too little treatment and other portions of the area receiving too much treatment, resulting in both types of losses described above.
Manufacturing environments, such as automobile production plant paint shops, plywood manufacturers, coated glass manufacturing, and other processing facilities typically use sprays to apply paint, adhesives, cleaning solutions, etc., at various steps in production processes. The ability to deliver a precise distribution of a sprayed solution in a specified period of time allows such plants to conserve resources, to reduce waste, and to optimize a production line for consistent production.
In recent years, the ability to quantify the effectiveness of military and homeland security detection equipment designed to detect pollutants, toxic chemicals and/or biological agents within an environment has further increased the need for a fast and effective determination of spray characteristics as applied to a target area. For example, Raman spectroscopy may now be used to scan an operational environment to detect trace amounts of unknown or suspect substances. In order to perform operational testing of such a system, the precise nature of a sprayed distribution within the target area of a test must be precisely known.
The performance instruments used to dispense a fluid in the form of a mist, or spray, is typically quantified in terms of volume per unit time. This, plus sprayer motion, results in a desired spray density and a mass median diameter (MMD) of droplets deposited upon a sprayed target. Spray density quantifies the total mass of all droplets deposited within a predetermined area. Mass median diameter is the diameter for which one-half of the mass sprayed upon a target is contributed by particles smaller than the MMD and one-half of the sprayed mass is contributed by particles larger than the MMD. For example, if 1001 mg of solution is sprayed upon a target, the mass median diameter is the particle size such that 505.5 mg are contributed by particles smaller than the MMD and 505.5 mg are contributed by particles larger than the MMD. Assuming that each droplet is substantially spherical, measures of spray density and MMD provide a measure of the coverage achieved with the spray.
Currently, there is no reliable mechanism for setting an instrument controlled spraying device to deliver a pre-set range of drop sizes with a pre-set quantity of chemical in order to meet prerequisite density and MMD parameters on a target area. Absent the precision in spraying, 1) droplets may be too small, resulting in spray drift and low spray density and poor coverage, and 2) droplets may be too large resulting in the same low spray density, and poor coverage. Further, the same control setting upon a spray device may result in a different as-sprayed result upon a target area due to a variety of external factors such as the temperature of the fluid being sprayed, the viscosity of the fluid at the current temperature, the distance of a target from the spray jet, the presence/absence of wind, high/low humidity, high/low ambient temperatures, and/or other factors which can cause portions of a spray to drift off and/or portions of the spray to evaporate prior to reaching a target.
The inability to control such spray characteristics via a spraying device, especially with respect to agricultural, forestry and military test operations, in which fluids are typically sprayed from aircraft and/or ground vehicles operating in relatively uncontrolled environments, requires that a spray's characteristics be sampled/monitored within a sprayed area in order to determine the spray characteristics achieved by a specific sprayed application. Such sampling/monitoring is also helpful in controlled environments such as production lines to periodically ascertain the as-is characteristics of an applied spray. In addition to the above, it is also an objective of the U.S. Department of Defense to evaluate military chemical detection systems by subjecting these systems to simulated field conditions where the spraying condition might, e.g., emulate the explosion of ordinance containing chemical warfare agents. Meeting these unusual conditions requires that the as-sprayed characteristics be sampled/monitored within a sprayed area in order to determine the spray characteristics.
Typically, such monitoring is performed by laying down paper or cardboard cards, commonly referred to as witness cards (WCs), at one or more locations within an area to which a spray is to be applied. The witness cards absorb the sprayed drops resulting in a fixed pattern of stains of varying sizes deposited on the cards. Thus, each card captures a representative sample of the spray at a location within the sprayed area. Once stained, a witness card is analyzed and the stain pattern is translated into a characterization of the spray in terms of spray density, MMD and other statistical parameters.
Unfortunately, conventional techniques for processing witness cards are quite limited. For example, one technique is to assess the droplet stains found within a plurality of portions of a given witness card, and found within a plurality of witness cards. A single witness card is typically sampled until a maximum of 15 portions/samples are processed or until information on 100 droplets is collected. Information related to the droplet stains is used to characterize the spray at the location of the witness card. By collecting information related to multiple witness cards distributed over an area subjected to a spraying operation, statistics related to the overall spraying are generated. U.S. Pat. No. 7,277,570 describes a more automated methodology for analyzing as-spayed witness cards that relies on electronic imagery and calibration techniques.
Notably, however, prior art witness card test spray methodologies require that the substance being sprayed be dyed so that droplets that stain the witness cards can be more easily seen or detected. However, dying a substance or liquid to be sprayed adds unnecessary expense in terms of both time and materials, may change the characteristics of the substance being sprayed, may adversely affect the performance of a given chemical detection system under test, or may cause different spray characteristics for different batches of the dyed liquid. For example, the U.S. Government has approved several “simulants” for use in spray tests. A simulant is a substance (e.g., a liquid or fluid) that may be used in place of another liquid, which may be too expensive or hazardous to use merely for testing purposes. By dyeing a simulant, the characteristics of the simulant may change, thereby further distancing a test spray from spray characteristics of a substance for which the simulant is being used.
Accordingly, there remains a need to provide improved witness card analysis techniques, especially where simulants are not dyed.